The within invention concerns a crane with a superstructure that rotates on a vertical axle, a boom coupled to the superstructure in such manner that it can luff on a horizontal axle, luffing equipment for raising and lowering the boom, and an operating ballast that counteracts the moment of the boom.
The problem that arises in the erecting of very long booms is that booms lying on the ground have a very large lever arm and consequently induce a large moment. To equalize this moment, an appropriately heavy counter-ballast must be positioned on the crane if the boom is to be erected at all. On the other hand, in crane operation such a large ballast is often not necessary, since in specific applications the crane boom is continually operated in relatively steep luffing position. To permit the crane boom nevertheless to be erected with a proportionally smaller operating ballast, it has already been proposed to provide in front of the crane superstructure a supplemental bracing that prevents the crane from tipping forward when the boom is erected. However, such supplemental bracings usually necessitate the providing of appropriate base plates.